The present invention disclosed herein relates to an amplifier structure and an amplification method thereof.
Linear amplifiers such as Class-A amplifiers provide an high output and high linearity, but have unsatisfied efficiency. In mobile communication systems, particularly, the efficiencies of linear amplifiers are further decreased. On the other hand, switching amplifiers such as Class-D amplifiers and Class-E amplifiers can provide high efficiency, but in the switching amplifiers, the kinds of inputs are limited to a signal having constant envelope characteristic in order for linearity to be guaranteed.
Therefore, research is being conducted on amplifier structures where linearity is guaranteed and high efficiency is obtained, as an example of which research on Class-S amplifiers are being attempted.
A typical Class-S amplifier structure 10 in FIG. 1 includes a delta-sigma modulator 11, a power amplifier 12, a band-pass filter 13, and a linearizer 14. The delta-sigma modulator 11 receives a Radio Frequency (RF) signal and converts the RF signal into a constant-envelope pulse signal to output the converted pulse signal to the power amplifier 12. The power amplifier 12 amplifies the received pulse signal to output the amplified pulse signal to the band-pass filter 13. The band-pass filter 13 selects only the amplified original signal from the amplified pulse signal to output the selected original signal to an antenna. The linearizer 14 corrects the nonlinear characteristic of the delta-sigma modulator 11 and the nonlinear characteristic of the power amplifier 12, in selective structure. Herein, a conversion method of converting to a constant envelope signal is limited by a signal reconstruction method corresponding to the band-pass filter 13, and the delta-sigma modulator 11 corresponds to a representative conversion method among several conversion methods.
In the typical Class-S amplifier structure 10 of FIG. 1, the delta-sigma modulator 11 is a band-pass delta-sigma modulator that receives an RF signal to operates, and generally operates at a speed higher by three times than an input center frequency. The delta-sigma modulator 11 has a limitation in that a high-speed delta-sigma modulator incapable of actual implementation is required for applying the typical Class-S amplifier structure 10 to a mobile communication service using a high RF. For example, WiMAX service using an RF of 3.5 GHz requires a delta-sigma modulator that operates at a speed higher than 10.5 GHz.
Moreover, in the typical Class-S amplifier structure 10, the power amplifier 12 is driven by the output signal of the delta-sigma modulator 11. However, since the output of the high-speed delta-sigma modulator 11 is in a wideband, it is difficult to implement the wideband input matching of the power amplifier 12 driven by the high-speed delta-sigma modulator 11.